How to use the watchgod.cli.run_function function in watchgod

def test_simple(mocker, tmpdir):
    mocker.patch('watchgod.cli.set_start_method')
    mocker.patch('watchgod.cli.sys.stdin.fileno')
    mocker.patch('os.ttyname', return_value='/path/to/tty')
    mock_run_process = mocker.patch('watchgod.cli.run_process')
    cli('tests.test_cli.foobar', str(tmpdir))
    mock_run_process.assert_called_once_with(
        Path(str(tmpdir)),
        run_function,
        args=('tests.test_cli.foobar', '/path/to/tty'),
        callback=callback
    )

def test_tty_os_error(mocker, tmpworkdir):
    mocker.patch('watchgod.cli.set_start_method')
    mocker.patch('watchgod.cli.sys.stdin.fileno', side_effect=OSError)
    mock_run_process = mocker.patch('watchgod.cli.run_process')
    cli('tests.test_cli.foobar')
    mock_run_process.assert_called_once_with(
        Path(str(tmpworkdir)),
        run_function,
        args=('tests.test_cli.foobar', '/dev/tty'),
        callback=callback
    )

def test_run_function(tmpworkdir):
    assert not tmpworkdir.join('sentinel').exists()
    run_function('tests.test_cli.foobar', None)
    assert tmpworkdir.join('sentinel').exists()

def test_run_function_tty(tmpworkdir):
    # could this cause problems by changing sys.stdin?
    assert not tmpworkdir.join('sentinel').exists()
    run_function('tests.test_cli.foobar', '/dev/tty')
    assert tmpworkdir.join('sentinel').exists()